This application is based upon Japanese Patent Application No. 2002-15694, filed on Jan. 24, 2002, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a vehicle air conditioner which has an automatic air-conditioning control function.
2. Related Art
An air conditioner, such as the one described above, uses a calculated value of a signal from a sunlight sensor for automatic control of the air-conditioning. The calculated value is obtained by a time constant process in which a detected value (pure value) from the sunlight sensor is modified to have a time constant. The time constant process is performed due to the following reasons.
When the vehicle travels along a valley between tall buildings on a sunny day, the sunlight incident into the vehicle is intermittent so that the detected value at the sunlight sensor varies dynamically so as to make the control of the air-conditioning unstable. Therefore, the time constant process is used to prevent the unstable condition of the automatic control of the air-conditioning by using the modified detected value of the sunlight sensor in the automatic control of the air-conditioning.
The time constant process is performed so that the calculated value (output value) is changed exponentially with respect to time when the detected value (pure value) changes. A time constant can be denoted the time (second) until change in the calculated value reaches a value of, for example, 63.2% with respect to change in the detected value of the sunlight sensor. When the time constant is large, the change in the calculated value is moderated with respect to change in the detected value.
In a laid-open patent application publication JP-A-H04-138910, the time constant process for the detected value by the sunlight sensor is performed in connection with change in an elevation angle of the sunlight incident into the vehicle in the automatic controllable air conditioner.
In a technical disclosure of DENSO CORPORATION No. 107, which was published on Mar. 15, 1996, the time constant process for the detected value by the sunlight sensor is performed in connection with the elevation angle of the sunlight incident into the vehicle and an outside air temperature of the vehicle.
The temperature feeling of the passenger, which is the feeling of the passenger indicating how much he/she feels the temperature, is changed in accordance with (1) the stream of air inside the vehicle, (2) the radiation of the sunlight or the like and (3) an environmental temperature of the passenger (inside air temperature).
A degree in time-rate change of the temperature feeling of the passenger changes in relation to the inside air temperature even if the radiation of the sunlight is in the same condition. The above-described prior arts do not take into consideration the fact that the inside air temperature influences the temperature feeling of the passenger. Therefore, in the conventional arts, a difference occurs between the control of the air-conditioning by the calculated value after the time constant process and the actual change in the temperature feeling of the passenger. As a result, the air-conditioning cannot follow the actual change in the temperature feeling of the passenger. More specifically, the control of a blow-out temperature of the conditioned air to be supplied to a passenger compartment or a blow-out mode to supply the conditioned air to the passenger compartment differs from the actual change in the temperature feeling of the passenger so as to make the air-conditioning uncomfortable or strange for the passenger.
Although the time constant is changed in connection with the outside air temperature in the latter prior art described above, it influences the heat load of the whole air-conditioning of the of the vehicle, but does not influence the temperature feeling of the passenger directly. Therefore, it still causes the difference between the actual change in the temperature feeling of the passenger and the control of the air-conditioning by the calculated value after the time constant process.
An object of the invention is to provide an improved vehicle air conditioner that performs air-conditioning following an actual change in a temperature feeling of a passenger that is influenced by an inside temperature in a vehicle so as to be comfortable for the passenger.
According to an aspect of the present invention, the air conditioner has time constant process means for performing a time constant process taking in consideration the inside temperature, which denotes a temperature inside the vehicle such as a temperature of the air inside the vehicle, as well as an elevation angle of the sunlight incident into the vehicle in an automatic air-conditioning control.
With this feature, the air conditioner can determine a time constant which matches the actual change in the temperature feeling of the passenger since it is determined using the inside temperature as well as the elevation angle of the sunlight. This is because a degree (speed) in time-rate change of the change in the temperature feeling of the passenger is influenced by not only the elevation angle of the sunlight but also the inside temperature. Therefore, the passenger can feel a comfortable air-conditioning.
The passenger feels the heat with respect to an increase of the inside temperature more sensitively. Therefore, it is preferable that the time constant is decreased in accordance with the increase of the inside temperature to meet the control of the air-conditioning with the change in the temperature feeling of the passenger more suitably.
Preferably, the time constant changes in accordance with the elevation angle of the sunlight. For example, the time constant has a minimum value at a predetermined angle of the elevation angle, and has a maximum value at another angle other than the predetermined angle of the elevation angle.
More specifically, the time constant has the minimum value at around 30xc2x0 of the elevation angle since the sunlight can reach a face portion of the passenger directly at the angle so that the temperature feeling of the passenger changes speedily in a short time. In this case, the control of the air-conditioning follows a sensitive change in the temperature feeling of the passenger with a quick change in the control of the air-conditioning.
When the elevation angle increases from around 30xc2x0, it is preferable that the time constant is increased since a sunlight amount is decreased which is directly incident to the face portion of the passenger.
Preferably, a degree in increase of the time constant with respect to increase of the elevation angle of the sunlight is decreased in accordance with increase of the inside temperature. This is because a slight increase of the sunlight causes a sensitive change in the temperature feeling of the passenger at a high inside temperature such as 30xc2x0 C. or more.
Other features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings.